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At the recent Eastpack Show in New York City, Debbie Lund, Director, Regional Sales & Marketing for Penn-Wheeling Cap and Closures, cornered me and asked why I never wrote about induction sealing metal caps. (Penn-Wheeling Cap and Closures is the leading manufacturer of metal caps and recently introduced a two-piece, plastic, child resistant closure). She pointed out that Penn-Wheeling Cap and Closures has several customers that are successfully using induction innerseals with metal caps. Enercon has never said that you could not use metal caps for induction sealing. We have sold several induction systems that are doing just that.
In a standard, induction sealing application, using a plastic cap, all of the electromagnetic field goes directly into the foil liner, melting the sealant layer and sealing the liner to the lip of the container. When using metal caps, the electromagnetic field is absorbed by the cap, which gets hot and transfers the heat to the foil inside the cap, thereby heating the foil by conduction. The results are the same, but the customer must be made aware of some of the potential dangers in this type of sealing. When using a metal cap, a special induction innerseal, with a low melt sealant, must be used. This type of liner is available from all of the major innerseal suppliers. Caution must be taken to insure that no one touches the metal closure immediately after it passes through the sealer, because it can be extremely hot and could cause serious burns if touched before it cools.
Other potential problems include overheating the cap, which could result in discoloration of the cap and possibly melting the threads, if used on a plastic bottle. Before the advent of the modern induction power supply, there was a very narrow window between getting the metal cap hot enough to sufficiently heat the foil and avoiding getting it too hot, resulting in the potential problems mentioned above. However, new, more efficient electronics provide a much larger operating window, which makes sealing metal closures much more user friendly.
As long as the customer is aware of the parameters involved in using metal caps in the induction process, it can be a very successful operation.
Originally appeared in: eNews: Induction Sealing Technology 3rd Quarter 2004
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 Enercon's Bill Zito inspects a recently sealed container in Enercon's inductio cap sealing laboratory.
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